VMS Help RTL Routines, MTH$, MTH$CSQRT, Returns  *Conan The Librarian (sorry for the slow response - running on an old VAX)

    OpenVMS usage:complex_number
    type:         F_floating complex
    access:       write only
    mechanism:    by value

    The complex square root of the complex-number argument. MTH$CSQRT
    returns an F-floating number.